Liquid crystal composition and liquid crystal display device

ABSTRACT

A liquid crystal composition having at least one or a suitable balance regarding at least two of characteristic such as high maximum temperature of a nematic phase, low minimum temperature thereof, small viscosity, suitable optical anisotropy, large dielectric anisotropy, large specific resistance, high stability to ultraviolet-light or heat, or large elastic constant; an AM-device having short response time, a large voltage holding ratio, low threshold voltage, a large contrast ratio, a negatively large DC brightness relaxation time constant and long-service-life. The liquid crystal composition contains a compound contributing to high stability to heat or ultraviolet-light as an additive component and a specific compound having positively large dielectric anisotropy, and a liquid crystal display device includes the composition. The composition may contain a specific compound having high maximum temperature or small viscosity as a second component or a specific compound having negative dielectric anisotropy as a third component.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serialno. 2014-153674, filed on Jul. 29, 2014 and Japan application serial no.2015-009403, filed on Jan. 21, 2015. The entirety of each of theabove-mentioned patent applications is hereby incorporated by referenceherein and made a part of this specification.

TECHNICAL FIELD

The invention relates to a liquid crystal composition, a liquid crystaldisplay device including the composition and so forth. In particular,the invention relates to a liquid crystal composition having a positivedielectric anisotropy and an active matrix (AM) device that includes thecomposition and has a mode such as a TN mode, an OCB mode, an IPS mode,an FFS mode or an FPA mode.

BACKGROUND ART

In a liquid crystal display device, a classification based on anoperating mode for liquid crystal molecules includes a phase change (PC)mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode,an electrically controlled birefringence (ECB) mode, an opticallycompensated bend (OCB) mode, an in-plane switching (IPS) mode, avertical alignment (VA) mode, a fringe field switching (FFS) mode and afield-induced photo-reactive alignment (FPA) mode. A classificationbased on a driving mode in the device includes a passive matrix (PM) andan active matrix (AM). The PM is classified into static, multiplex andso forth, and the AM is classified into a thin film transistor (TFT), ametal insulator metal (MIM) and so forth. The TFT is further classifiedinto amorphous silicon and polycrystal silicon. The latter is classifiedinto a high temperature type and a low temperature type according to aproduction process. A classification based on a light source includes areflective type utilizing natural light, a transmissive type utilizingbacklight and a transflective type utilizing both the natural light andthe backlight.

The liquid crystal display devices include a liquid crystal compositionhaving the nematic phase. The composition has suitable characteristics.An AM device having good characteristics can be obtained by improvingthe characteristics of the composition. Table 1 below summarizes arelationship of characteristics between two aspects. The characteristicsof the composition will be further described based on a commerciallyavailable AM device. A temperature range of the nematic phase relates toa temperature range in which the device can be used. A preferred maximumtemperature of the nematic phase is approximately 70° C. or higher, anda preferred minimum temperature of the nematic phase is approximately−10° C. or lower. Viscosity of the composition relates to a responsetime in the device. A short response time is preferred for displayingmoving images on the device. A shorter response time even by onemillisecond is desirable. Accordingly, a small viscosity in thecomposition is preferred. A small viscosity at a low temperature isfurther preferred. An elastic constant of the composition relates tocontrast in the device. In order to increase the contrast in the device,a large elastic constant in the composition is further preferred.

TABLE 1 General Characteristics of Composition and AM Device GeneralCharacteristics General Characteristics No. of Composition of AM Device1 Wide temperature range Wide usable of a nematic phase temperaturerange 2 Small viscosity Short response time 3 Suitable opticalanisotropy Large contrast ratio 4 Large positive or negative Lowthreshold voltage and small dielectric anisotropy electric powerconsumption Large contrast ratio 5 Large specific resistance Largevoltage holding ratio and large contrast ratio 6 High stability toultraviolet light Long service life and heat 7 Large elastic constantLarge constant ratio and short response time

An optical anisotropy of a composition relates to a contrast ratio inthe device. According to a mode of the device, a large opticalanisotropy or a small optical anisotropy, more specifically, a suitableoptical anisotropy is required. A product (Δn×d) of the opticalanisotropy (Δn) of the composition and a cell gap (d) of the device isdesigned so as to maximize the contrast ratio. A suitable value of theproduct depends on a type of the operating mode. The suitable value isapproximately 0.45 micrometer in a device having a mode such as the TNmode. In the above case, a composition having a large optical anisotropyis preferred for a device having a small cell gap. A large dielectricanisotropy in the composition contributes to a low threshold voltage, asmall electric power consumption and a large contrast ratio in thedevice. Accordingly, the large dielectric anisotropy is preferred. Alarge specific resistance in the composition contributes to a largevoltage holding ratio and a large contrast ratio in the device.Accordingly, a composition having a large specific resistance at roomtemperature and also at a temperature close to the maximum temperatureof the nematic phase in an initial stage is preferred. A compositionhaving a large specific resistance at room temperature and also at atemperature close to the maximum temperature of the nematic phase evenafter the device has been used for a long period of time is preferred.Stability of the composition to ultraviolet light and heat relates to aservice life of the liquid crystal display device. In a case where thestability is high, the device has a long service life. Suchcharacteristics are preferred for an AM device for use in a liquidcrystal projector and a liquid crystal television and so forth.

As the liquid crystal display device is used for a long time, imagepersistence is caused by accumulation of electric charge in part ofpicture elements. Then, in order to prevent the image persistence, anadditive for accelerating discharge of the electric charge accumulatedin the picture element has been studied. A DC brightness relaxation timeconstant described in Patent literature No. 1 has been used as a measureof discharge. As a result, the liquid crystal display device containingthe liquid crystal composition in which compound (1) described herein isadded has been found to have a negatively large DC brightness relaxationtime constant. In addition, compound (1) is disclosed by Patentliterature No. 2.

CITATION LIST Patent Literature

Patent literature No. 1: JP 2012-053394 A.

Patent literature No. 2: JP S47-027981 A.

SUMMARY OF INVENTION Technical Problem

This invention provides a liquid crystal composition satisfying at leastone of characteristics such as a high maximum temperature of a nematicphase, a low minimum temperature of the nematic phase, a smallviscosity, a suitable optical anisotropy, a large dielectric anisotropy,a large specific resistance, a high stability to ultraviolet light, ahigh stability to heat and a large elastic constant. This invention alsoprovides a liquid crystal composition having a suitable balanceregarding at least two of the characteristics. This invention furtherprovides a liquid crystal display device including such a composition.This invention further provides an AM device having characteristics suchas a short response time, a large voltage holding ratio, a low thresholdvoltage, a large contrast ratio, a negatively large DC brightnessrelaxation time constant and a long service life.

Solution to Problem

The invention concerns a liquid crystal composition that has a positivedielectric anisotropy and a nematic phase, and contains at least onecompound selected from the group of compounds represented by formula (1)as an additive component and at least one compound from the group ofcompounds represented by formula (2) as a first component, and a liquidcrystal display device including the composition:

wherein, in formula (1), R¹ is hydrogen or alkyl having 1 to 15 carbons;R², R³, R⁴ and R⁵ are independently hydrogen or alkyl having 1 to 4carbons; ring A is a polyvalent group derived from benzene orcyclohexane by eliminating hydrogen; a is 3 or 4; and

in formula (2), R⁶ is alkyl having 1 to 12 carbons, alkoxy having to 12carbons or alkenyl having 2 to 12 carbons; ring B is 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene,2,6-difluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl ortetrahydropyran-2,5-diyl; Z¹ is a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are independently hydrogen or fluorine;Y¹ is fluorine, chlorine, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, alkoxy having 1 to12 carbons in which at least one of hydrogen is replaced by fluorine orchlorine, or alkenyloxy having 2 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; and b is 1, 2, 3 or 4.

The invention also concerns use of the liquid crystal composition in aliquid crystal display device.

Advantageous Effects of Invention

An advantage of the invention is to provide a liquid crystal compositionsatisfying at least one of characteristics such as a high maximumtemperature of a nematic phase, a low minimum temperature of the nematicphase, a small viscosity, a suitable optical anisotropy, a largedielectric anisotropy, a large specific resistance, a high stability toultraviolet light, a high stability to heat and a large elasticconstant. Another advantage is a liquid crystal composition having asuitable balance regarding at least two of the characteristics. Afurther advantage is a liquid crystal display device including such acomposition. A still further advantage is an AM device havingcharacteristics such as a short response time, a large voltage holdingratio, a low threshold voltage, a large contrast ratio, a negativelylarge DC brightness relaxation time constant and a long service life.

DESCRIPTION OF EMBODIMENTS

Usage of terms herein is as described below. “Liquid crystalcomposition” and “liquid crystal display device” may be occasionallyabbreviated as “composition” and “device,” respectively. “Liquid crystaldisplay device” is a generic term for a liquid crystal display panel anda liquid crystal display module. “Liquid crystal compound” is a genericterm for a compound having a liquid crystal phase such as a nematicphase and a smectic phase and a compound having no liquid crystal phasebut to be mixed with the composition for the purpose of adjustingcharacteristics such as a temperature range of the nematic phase,viscosity and dielectric anisotropy. The compound has a six-memberedring such as 1,4-cyclohexylene and 1,4-phenylene, and has rod-likemolecular structure. “polymerizable compound” is added to the compoundfor the purpose of producing a polymer in the composition. At least onecompound selected from the group of compounds represented by formula (1)may be occasionally abbreviated as “compound (1).” “Compound (1)” meansone compound represented by formula (1), a mixture of two compounds or amixture of three or more compounds represented thereby. A same ruleapplies to any other compound represented by any other formula.

The liquid crystal composition is prepared by mixing a plurality ofliquid crystal compounds. A ratio (content) of the liquid crystalcompounds is expressed in terms of weight percent (% by weight) based onthe weight of the liquid crystal composition. An additive such as anoptically active compound, an antioxidant, an ultraviolet lightabsorber, a dye, an antifoaming agent, a polymerizable compound, apolymerization initiator and a polymerization inhibitor is added to theliquid crystal composition, when necessary. A ratio (amount of addition)of the additive is expressed in terms of weight percent (% by weight)based on the weight of the liquid crystal composition in a mannersimilar to the ratio of the liquid crystal compounds. Weight parts permillion (ppm) may be occasionally used. A ratio of the polymerizationinitiator and the polymerization inhibitor is exceptionally expressedbased on the weight of the polymerizable compound.

“Higher limit of the temperature range of the nematic phase” may beoccasionally abbreviated as “maximum temperature.” “Lower limit of thetemperature range of the nematic phase” may be occasionally abbreviatedas “minimum temperature.” An expression “having a large specificresistance” means that the composition has a large specific resistanceat room temperature and also at a temperature close to the maximumtemperature of the nematic phase in an initial stage, and that thecomposition has a large specific resistance at room temperature and alsoat a temperature close to the maximum temperature of the nematic phaseeven after the device has been used for a long period of time. Anexpression “having a large voltage holding ratio” means that the devicehas a large voltage holding ratio at room temperature and also at atemperature close to the maximum temperature of the nematic phase in aninitial stage, and that the device has a large voltage holding ratio atroom temperature and also at a temperature close to the maximumtemperature of the nematic phase even after the device has been used fora long period of time.

An expression “at least one of ‘A’” means that the number of ‘A’ isarbitrary. An expression “at least one of ‘A’ may be replaced by ‘B’”means that a position of ‘A’ is arbitrary when the number of ‘A’ is one,and positions thereof when ‘A’ is two or more can also be selectedwithout restriction. A same rule applies also to an expression “at leastone of ‘A’ is replaced by ‘B’.”

A symbol of terminal group R⁶ is used for a plurality of compounds inchemical formulas of component compounds. In the compounds, two groupsrepresented by two of arbitrary R⁶ may be identical or different. In onecase, for example, R⁶ of compound (2) is ethyl and R⁶ of compound (2-1)is ethyl. In another case, R⁶ of compound (2) is ethyl and R⁶ ofcompound (2-1) is propyl. A same rule applies also to a symbol of anyother terminal group or the like. In formula (2), when b is 2, two ofring B exist. In the compound, two rings represented by two of ring Bmay be identical or different. A same rule applies also to two ofarbitrary ring B when b is larger than 2. A same rule applies also toZ², ring C or the like.

Then, 2-fluoro-1,4-phenylene means two of divalent groups describedbelow. In the chemical formula, fluorine may be leftward (L) orrightward (R). A same rule applies also to an asymmetrical divalentgroup such as tetrahydropyran-2,5-diyl. A same rule applies also to abonding group such as carbonyloxy (—COO— and —OCO—).

The invention includes the items described below.

Item 1. A liquid crystal composition that has a positive dielectricanisotropy and a nematic phase, and contains at least one compoundselected from the group of compounds represented by formula (1) as anadditive component and at least one compound from the group of compoundsrepresented by formula (2) as a first component:

wherein, in formula (1), R¹ is hydrogen or alkyl having 1 to 15 carbons;R², R³, R⁴ and R⁵ are independently hydrogen or alkyl having 1 to 4carbons; ring A is a polyvalent group derived from benzene orcyclohexane by eliminating hydrogen; a is 3 or 4; and

in formula (2), R⁶ is alkyl having 1 to 12 carbons, alkoxy having to 12carbons or alkenyl having 2 to 12 carbons; ring B is 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene,2,6-difluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl ortetrahydropyran-2,5-diyl; Z¹ is a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are independently hydrogen or fluorine;Y¹ is fluorine, chlorine, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, alkoxy having 1 to12 carbons in which at least one of hydrogen is replaced by fluorine orchlorine, or alkenyloxy having 2 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; and b is 1, 2, 3 or 4.

Item 2. The liquid crystal composition according to item 1, containing acompound represented by formula (1-1) or formula (1-2) as the additivecomponent:

Item 3. The liquid crystal composition according to item 1 or 2, whereina ratio of the additive component is in the range of 0.005% by weight to1% by weight based on the weight of the liquid crystal composition.

Item 4. The liquid crystal composition according to any one of items 1to 3, containing at least one compound selected from the group ofcompounds represented by formula (2-1) to (2-35) as the first component:

wherein, in formula (2-1) to (2-35), R⁶ is alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons or alkenyl having 2 to 12 carbons.

Item 5. The liquid crystal composition according to any one of items 1to 4, wherein a ratio of the first component is in the range of 10% byweight to 90% by weight based on the weight of the liquid crystalcomposition.

Item 6. The liquid crystal composition according to any one of items 1to 5, containing at least one compound selected from the group ofcompounds represented by formula (3) as a second component:

wherein, in formula (3), R⁷ and R⁸ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, alkyl having 1 to 12 carbons in which at least one of hydrogenis replaced by fluorine or chlorine, or alkenyl having 2 to 12 carbonsin which at least one of hydrogen is the replaced by fluorine orchlorine; ring C and ring D are independently 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene or 2,5-difluoro-1,4-phenylene; Z²is a single bond, ethylene or carbonyloxy; and c is 1, 2 or 3.

Item 7. The liquid crystal composition according to any one of items 1to 6, containing at least one compound selected from the group ofcompounds represented by formula (3-1) to (3-13) as the secondcomponent:

wherein, in formula (3-1) to formula (3-13), R⁷ and R⁸ are independentlyalkyl having 1 to 12 carbons, alkoxy having 1 to 12 carbons, alkenylhaving 2 to 12 carbons, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, or alkenyl having 2to 12 carbons in which at least one of hydrogen is replaced by fluorineor chlorine.

Item 8. The liquid crystal composition according to item 6 or 7, whereina ratio of the second component is in the range of 10% by weight to 90%by weight based on the weight of the liquid crystal composition.

Item 9. The liquid crystal composition according to any one of items 1to 8, containing at least one compound selected from the group ofcompounds represented by formula (4) as a third component:

wherein, in formula (4), R⁹ and R¹⁰ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; ring E and ring G areindependently 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene,1,4-phenylene in which at least one of hydrogen is replaced by fluorineor chlorine, or tetrahydropyran-2,5-diyl; ring F is2,3-difluoro-1,4-phenylene, 2-chloro-3-fluoro-1,4-phenylene,2,3-difluoro-5-methyl-1,4-phenylene, 3,4,5-trifluoronaphthalene-2,6-diylor 7,8-difluorochroman-2,6-diyl; Z³ and Z⁴ are independently a singlebond, ethylene, carbonyloxy or methyleneoxy; d is 1, 2 or 3, and e is 0or 1; and a sum of d and e is 3 or less.

Item 10. The liquid crystal composition according to any one of items 1to 9, containing at least one compound selected from the group ofcompounds represented by formula (4-1) to formula (4-21) as the thirdcomponent:

wherein, in formula (4-1) to formula (4-21), R⁹ and R¹⁰ areindependently alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, alkenyloxy having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine.

Item 11. The liquid crystal composition according to item 9 or 10,wherein a ratio of the third component is in the range of 3% by weightto 25% by weight based on the weight of the liquid crystal composition.

Item 12. The liquid crystal composition according to any one of items 1to 11, wherein a maximum temperature of a nematic phase is 70° C. orhigher, optical anisotropy (measured at 25° C.) at a wavelength of 589nanometers is 0.07 or more, and dielectric anisotropy (measured at 25°C.) at a frequency of 1 kHz is 2 or more.

Item 13. A liquid crystal display device including the liquid crystalcomposition according to any one of items 1 to 12.

Item 14. The liquid crystal display device according to item 13, whereinan operating mode of the liquid crystal display device includes a TNmode, an ECB mode, an OCB mode, an IPS mode, an FFS mode or an FPA mode,and a driving mode of the liquid crystal display device includes anactive matrix mode.

Item 15. Use of the liquid crystal composition according to any one ofitems 1 to 12 in a liquid crystal display device.

The invention further includes the following items: (a) the composition,further containing at least one additive such as an optically activecompound, an antioxidant, an ultraviolet light absorber, a dye, anantifoaming agent, a polymerizable compound, a polymerization initiatoror a polymerization inhibitor; (b) an AM device including thecomposition; (c) the composition, further including the polymerizablecompound, and a polymer sustained alignment (PSA) mode AM device,including the composition; (d) a polymer sustained alignment (PSA) modeAM device, wherein the device includes the composition, and thepolymerizable compound in the composition is polymerized; (e) a device,including the composition and having a PC, TN, STN, ECB, OCB, IPS, FFSor FPA mode; (f) a transmissive device including the composition; (g)use of the composition as the composition having the nematic phase; and(h) use as an optical active composition by adding the optically activecompound to the composition.

The composition of the invention will be described in the followingorder. First, a constitution of component compounds in the compositionwill be described. Second, main characteristics of the componentcompounds and main effects of the compounds on the composition will bedescribed. Third, a combination of components in the composition, apreferred ratio of the component and the basis thereof will bedescribed. Fourth, a preferred embodiment of the component compoundswill be described. Fifth, a preferred component compound will be shown.Sixth, an additive that may be added to the composition will bedescribed. Seventh, a method for synthesizing the component compoundwill be described. Last, an application of the composition will bedescribed.

First, the constitution of the component compounds in the compositionwill be described. The composition of the invention is classified intocomposition A and composition B. Composition A may further contain anyother liquid crystal compound, the additive or the like in addition tothe liquid crystal compound selected from compound (2), compound (3) andcompound (4). “Any other liquid crystal compound” means a liquid crystalcompound different from compound (2), compound (3) and compound (4).Such a compound is mixed with the composition for the purpose of furtheradjusting the characteristics of the composition. The additive includescompound (1), the optically active compound, the antioxidant, theultraviolet light absorber, the dye, the antifoaming agent, thepolymerizable compound, the polymerization initiator and thepolymerization inhibitor.

Composition B consists essentially of liquid crystal compounds selectedfrom compound (2), compound (3) and compound (4). A term “essentially”means that the composition may contain the additive, but does notcontain any other liquid crystal compound. An example of composition Bincludes a component containing compound (1), compound (2) and compound(3) as essential components. Composition B has a smaller number ofcomponents than composition A has. Composition B is preferred tocomposition A in view of cost reduction. Composition A is preferred tocomposition B in view of possibility of further adjusting thecharacteristics of the composition by mixing any other liquid crystalcompound.

Second, the main characteristics of the component compound and the maineffects of the compounds on the characteristics of the composition willbe described. The main characteristics of the component compounds aresummarized in Table 2 on the basis of advantageous effects of theinvention. In Table 2, a symbol L stands for “large or high,” a symbol Mstands for “medium,” and a symbol S stands for “small or low.” Thesymbols L, M and S represent a classification based on a qualitativecomparison among the component compounds, and 0 (zero) means that avalue is zero or nearly zero.

TABLE 2 Characteristics of Compounds Compounds Compound (2) Compound (3)Compound (4) Maximum temperature S to L S to L S to M Viscosity M to L Sto M L Optical anisotropy M to L S to L M to L Dielectric anisotropy Sto L¹⁾ 0 L²⁾ Specific resistance L L L ¹⁾Compound having positivedielectric anisotropy. ²⁾Compound having negative dielectric anisotropy

Upon mixing the component compounds to the composition, the main effectsof the component compounds on the characteristics of the composition areas described below. Compound (1) contributes to a high stability to heator ultraviolet light. Compound (1) also contributes to a negativelylarge DC brightness relaxation time constant. Compound (1) have noinfluence on the characteristics such as the maximum temperature, theoptical anisotropy and the dielectric anisotropy. Compound (2) increasesthe dielectric anisotropy. Compound (3) increases the maximumtemperature or decreases the minimum temperature. Compound (4) increasesa dielectric constant in a minor axis direction.

Third, the combination of component compound in the composition, thepreferred ratio of the component compounds and the basis thereof will bedescribed. The preferred combination of components in the compositionincludes a combination of compound (1) and compound (2), a combinationof compound (1), compound (2) and compound (3), a combination ofcompound (1), compound (2) and compound (4), or a combination ofcompound (1), compound (2), compound (3) and compound (4). A furtherpreferred combination is the combination of compound (1), compound (2)and compound (3), or the combination of compound (1), compound (2),compound (3) and compound (4).

A preferred ratio of compound (1) is approximately 0.005% by weight ormore for contributing to the high stability to heat or ultraviolet lightand contributing to the negatively large DC brightness relaxation timeconstant, and approximately 1% by weight or less for decreasing theminimum temperature. A further preferred ratio is in the range ofapproximately 0.01% to approximately 0.5% by weight. A particularlypreferred ratio is in the range of approximately 0.03% to approximately0.3% by weight.

A preferred ratio of compound (2) is approximately 10% by weight or morefor increasing the dielectric anisotropy, and approximately 90% byweight or less for decreasing the minimum temperature or decreasing theviscosity. A further preferred ratio is in the range of approximately20% by weight to approximately 80% by weight. A particularly preferredratio is in the range of approximately 30% by weight to approximately70% by weight.

A preferred ratio of compound (3) is in the range of approximately 10%by weight or more for increasing the maximum temperature or decreasingthe viscosity, and approximately 90% by weight or less for increasingthe dielectric anisotropy. A further preferred ratio is in the range ofapproximately 20% by weight to approximately 80% by weight. Aparticularly preferred ratio is in the range of approximately 25% byweight to approximately 70% by weight.

A preferred ratio of compound (4) is approximately 3% by weight or morefor increasing the dielectric anisotropy, and approximately 25% byweight or less for decreasing the minimum temperature. A furtherpreferred ratio is in the range of approximately 5% by weight toapproximately 20% by weight. A particularly preferred ratio is in therange of approximately 5% by weight to approximately 15% by weight.

Fourth, the preferred embodiment of the component compounds will bedescribed. In formula (1), R¹ is hydrogen or alkyl having 1 to 15carbons. Preferred R¹ is hydrogen or methyl. R², R³, R⁴ and R⁵ areindependently hydrogen or alkyl having 1 to 4 carbons. Preferred R², R³,R⁴ or R⁵ is hydrogen or methyl.

Ring A is a polyvalent group derived from benzene or cyclohexane byeliminating hydrogen. Then, a is 3 or 4. Accordingly, ring A istrivalent or tetravalent. Preferred ring A is a trivalent group or atetravalent group derived from benzene. Further preferred ring A is atetravalent group derived from benzene.

In formula (2), formula (3) and formula (4), R⁶ is alkyl having 1 to 12carbons, alkoxy having 1 to 12 carbons, or alkenyl having 2 to 12carbons. Preferred R⁶ is alkyl having 1 to 12 carbons for increasing thestability to ultraviolet light or heat. R⁷ and R⁸ are independentlyalkyl having 1 to 12 carbons, alkoxy having 1 to 12 carbons, alkenylhaving 2 to 12 carbons, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, or alkenyl having 2to 12 carbons in which at least one of hydrogen is replaced by fluorineor chlorine. Preferred R⁷ or R⁸ is alkenyl having 2 to 12 carbons fordecreasing the viscosity, and alkyl having 1 to 12 carbons forincreasing the stability. R⁹ and R¹⁰ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, alkenyloxy having 2 to 12 carbons, or alkyl having 1 to 12carbons in which at least one of hydrogen is replaced by fluorine orchlorine. Preferred R⁹ or R¹⁰ is alkyl having 1 to 12 carbons forincreasing the stability, and alkoxy having 1 to 12 carbons forincreasing the dielectric anisotropy.

Preferred alkyl is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptylor octyl. Further preferred alkyl is ethyl, propyl, butyl, pentyl orheptyl for decreasing the viscosity.

A preferred example of alkyl in which at least one of hydrogen isreplaced by fluorine or chlorine, includes fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl,7-fluoroheptyl or 8-fluorooctyl. A further preferred example includes2-fluoroethyl, 3-fluoropropyl, 4-fluorobuty or 5-fluoropentyl forincreasing the dielectric anisotropy.

Preferred alkoxy is methoxy, ethoxy, propoxy, butoxy, pentyloxy,hexyloxy or heptyloxy. Further preferred alkoxy is methoxy or ethoxy fordecreasing the viscosity.

Preferred alkenyl is vinyl, 1-propenyl, 2-propenyl, 1-butenyl,2-butenyl, 3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl or 5-hexenyl. Furtherpreferred alkenyl is vinyl, 1-propenyl, 3-butenyl or 3-pentenyl fordecreasing the viscosity. A preferred configuration of —CH═CH— in thealkenyl depends on a position of a double bond. Trans is preferred inalkenyl such as 1-propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, 3-pentenyland 3-hexenyl for decreasing the viscosity, for instance. Cis ispreferred in alkenyl such as 2-butenyl, 2-pentenyl and 2-hexenyl. In thealkenyl, straight-chain alkenyl is preferred to branched-chain alkenyl.

A preferred example of alkenyl in which at least one of hydrogen isreplaced by fluorine or chlorine includes 2,2-difluorovinyl,3,3-difluoro-2-propenyl, 4,4-difluoro-3-butenyl, 5,5-difluoro-4-pentenylor 6,6-difluoro-5-hexenyl. A further preferred example includes2,2-difluorovinyl or 4,4-difluoro-3-butenyl for decreasing theviscosity.

Preferred alkenyloxy is vinyloxy, allyloxy, 3-butenyloxy, 3-pentenyloxyor 4-pentenyloxy. Further preferred alkenyloxy is allyloxy or3-butenyloxy for decreasing the viscosity.

Then, b is 1, 2, 3 or 4. Preferred b is 2 for decreasing the minimumtemperature, and 3 for increasing the dielectric anisotropy. Then, c is1, 2 or 3. Preferred c is 1 for decreasing the viscosity, and 2 or 3 forincreasing the maximum temperature. Then, d is 1, 2 or 3, e is 0 or 1,and a sum of d and e is 3 or less. Preferred d is 1 for decreasing theviscosity, and 2 or 3 for increasing the maximum temperature. Preferrede is 0 for decreasing the viscosity, and 1 for decreasing the minimumtemperature.

Z¹ is a single bond, ethylene, carbonyloxy or difluoromethyleneoxy.Preferred Z¹ is a single bond for decreasing the viscosity, anddifluoromethyleneoxy for increasing the dielectric anisotropy. Z² is asingle bond, ethylene, or carbonyloxy. Preferred Z² is a single bond fordecreasing the viscosity. Z³ and Z⁴ are independently a single bond,ethylene, carbonyloxy or methyleneoxy. Preferred Z³ or Z⁴ is a singlebond for decreasing the viscosity, and methyleneoxy for increasing thedielectric anisotropy.

Ring B is 1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene,2,3-difluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene,pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl or tetrahydropyran-2,5-diyl.Preferred ring B is 1,4-phenylene or 2-fluoro-1,4-phenylene forincreasing the optical anisotropy. Ring C and ring D are independently1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene or2,5-difluoro-1,4-phenylene. Preferred ring C or ring D is1,4-cyclohexylene for decreasing the viscosity, or 1,4-phenylene forincreasing the optical anisotropy.

Ring E and ring G are independently 1,4-cyclohexylene,1,4-cyclohexenylene, 1,4-phenylene, 1,4-phenylene in which at least oneof hydrogen is replaced by fluorine or chlorine, ortetrahydropyran-2,5-diyl. A preferred example of “1,4-phenylene in whichat least one of hydrogen is replaced by fluorine or chlorine” includes2-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or2-chloro-3-fluoro-1,4-phenylene. Preferred ring E or ring G is1,4-cyclohexylene for decreasing the viscosity, tetrahydropyran-2,5-diylfor increasing the dielectric anisotropy and 1,4-phenylene forincreasing the optical anisotropy. Ring F is 2,3-difluoro-1,4-phenylene,2-chloro-3-fluoro-1,4-phenylene, 2,3-difluoro-5-methyl-1,4-phenylene,3,4,5-trifluoronaphthalene-2,6-diyl or 7,8-difluorochroman-2,6-diyl.Preferred ring F is 2,3-difluoro-1,4-phenylene for increasing thedielectric anisotropy. With regard to a configuration of1,4-cyclohexylene, trans is preferred to cis for increasing the maximumtemperature. Tetrahydropyran-2,5-diyl includes:

X¹ and X² are independently hydrogen or fluorine. Preferred X¹ or X² isfluorine for increasing the dielectric anisotropy.

Y¹ is fluorine, chlorine, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, alkoxy having 1 to12 carbons in which at least one of hydrogen is replaced by fluorine orchlorine, or alkenyloxy having 2 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine. A preferred example ofalkyl in which at least one of hydrogen is replaced by fluorine orchlorine, includes trifluoromethyl. A preferred example of alkoxy inwhich at least one of hydrogen is replaced by fluorine or chlorine,includes trifluoromethoxy. A preferred example of alkenyloxy in which atleast one of hydrogen is replaced by fluorine or chlorine, includestrifluorovinyloxy. Preferred Y¹ is fluorine or trifluoromethyl. Furtherpreferred Y¹ is fluorine for decreasing the minimum temperature.

Fifth, the preferred component compound will be shown. Preferredcompound (1) includes compound (1-1) and compound (1-2) as described initem 2. Further preferred compound (1) includes compound (1-1).

Preferred compound (2) includes compound (2-1) to compound (2-35) asdescribed in item 4. In the compounds, at least one of the secondcomponents preferably includes compound (2-4), compound (2-12), compound(2-14), compound (2-15), compound (2-17), compound (2-18), compound(2-23), compound (2-27), compound (2-29) or compound (2-30). At leasttwo of the second components preferably includes a combination ofcompound (2-12) and compound (2-15), a combination of compound (2-14)and compound (2-27), a combination of compound (2-18) and compound(2-24), a combination of compound (2-18) and compound (2-29), acombination of compound (2-24) and compound (2-29) or a combination ofcompound (2-29) and compound (2-30).

Preferred compound (3) includes compound (3-1) to compound (3-13) asdescribed in item 7. In the compounds, at least one of the thirdcomponent preferably includes compound (3-1), compound (3-3), compound(3-5), compound (3-6), compound (3-7) or compound (3-13). At least twoof the third components preferably includes a combination of compound(3-1) and compound (3-3), a combination of compound (3-1) and compound(3-5) or a combination of compound (3-1) and compound (3-7).

Preferred compound (4) includes compound (4-1) to compound (4-21) asdescribed in item 10. In the compounds, at least one of the fourthcomponent preferably includes compound (4-1), compound (4-4), compound(4-5), compound (4-7), compound (4-10) or compound (4-15). At least twoof the fourth components preferably includes a combination of compound(4-1) and a compound (4-7), a combination of compound (4-1) and compound(4-15), a combination of compound (4-4) and compound (4-7), acombination of compound (4-4) and compound (4-15), a combination ofcompound (4-5) and compound (4-7) or a combination of compound (4-5) andcompound (4-10).

Sixth, the additive that may be added to the composition will bedescribed. Such an additive includes the optically active compound, theantioxidant, the ultraviolet light absorber, the dye, the antifoamingagent, the polymerizable compound, the polymerization initiator and thepolymerization inhibitor. The optically active compound is added to thecomposition for the purpose of inducing a helical structure of a liquidcrystal molecule to give a twist angle. An example of such a compoundincludes compound (5-1) to compound (5-5). A preferred ratio of theoptically active compound is approximately 5% by weight or less. Afurther preferred ratio is in the range of approximately 0.01% by weightto approximately 2% by weight.

The antioxidant is added to the composition for the purpose ofpreventing a decrease in the specific resistance caused by heating inair, or maintaining a large voltage holding ratio at room temperatureand also at a temperature close to the maximum temperature even afterthe device has been used for a long period of time. A preferred exampleof the antioxidant includes compound (6) where t is an integer from 1 to9.

In compound (6), preferred t is 1, 3, 5, 7 or 9. Further preferred t is7. Compound (6) where t is 7 is effective in maintaining a large voltageholding ratio at room temperature and also at a temperature close to themaximum temperature even after the device has been used for a longperiod of time because such compound (6) has a small volatility. Apreferred ratio of the antioxidant is approximately 50 ppm or more forachieving the effect thereof, and approximately 600 ppm or less foravoiding a decrease in the maximum temperature or avoiding an increasein the minimum temperature. A further preferred ratio is in the range ofapproximately 100 ppm to approximately 300 ppm.

A preferred example of the ultraviolet light absorber includes abenzophenone derivative, a benzoate derivative and a triazolederivative. A light stabilizer such as an amine having steric hindranceis also preferred. A preferred ratio of the ultraviolet light absorberor the stabilizer is approximately 50 ppm or more for achieving theeffect thereof, and approximately 10,000 ppm or less for avoiding adecrease in the maximum temperature or avoiding an increase in theminimum temperature. A further preferred ratio is in the range ofapproximately 100 ppm to approximately 10,000 ppm.

A dichroic dye such as an azo dye or an anthraquinone dye is added tothe composition to be adapted for a device having a guest host (GH)mode. A preferred ratio of the dye is in the range of approximately0.01% by weight to approximately 10% by weight. The antifoaming agentsuch as dimethyl silicone oil or methyl phenyl silicone oil is added tothe composition for preventing foam formation. A preferred ratio of theantifoaming agent is approximately 1 ppm or more for achieving theeffect thereof, and approximately 1,000 ppm or less for preventing poordisplay. A further preferred ratio is in the range of approximately 1ppm to approximately 500 ppm.

The polymerizable compound is added to the composition to be adapted forthe polymer sustained alignment (PSA) mode device. A preferred exampleof the polymerizable compound includes a compound containing apolymerizable group, such as an acrylate, a methacrylate, a vinylcompound, a vinyloxy compound, a propenyl ether, an epoxy compound(oxirane and oxetane) and a vinyl ketone. A further preferred exampleincludes a derivative of acrylate or methacrylate. A preferred ratio ofthe polymerizable compound is in the range of approximately 0.05% byweight or more for achieving the effect thereof and approximately 10% byweight or less for preventing poor display. A further preferred ratio isin the range of approximately 0.1% by weight to approximately 2% byweight. The polymerizable compound is polymerized by irradiation withultraviolet light. The polymerizable compound may be polymerized in thepresence of an initiator such as a photopolymerization initiator.Suitable conditions for polymerization, suitable types of the initiatorand suitable amounts are known to those skilled in the art and aredescribed in literature. For example, Irgacure 651 (registeredtrademark; BASF), Irgacure 184 (registered trademark; BASF) or Darocur1173 (registered trademark; BASF), each being a photoinitiator, issuitable for radical polymerization. A preferred ratio of thephotopolymerization initiator is in the range of approximately 0.1% byweight to approximately 5% by weight based on the weight of thepolymerizable compound. A further preferred ratio is in the range ofapproximately 1% by weight to approximately 3% by weight.

When the polymerizable compound is stored, the polymerization inhibitormay be added in order to prevent polymerization. The polymerizablecompound is ordinarily added to the composition without eliminating thepolymerization inhibitor. An example of the polymerization inhibitorincludes hydroquinone, a hydroquinone derivative such as methylhydroquinone, 4-tert-butyl-catechol, 4-methoxyphenol and phenothiazine.

Seventh, the methods for synthesizing the component compounds will bedescribed. The compounds can be prepared by a known method. Examples ofsynthetic methods will be presented. Compound (1-1) is prepared by themethod described in JP S47-027981 A. Compound (2-2) and compound (2-8)are prepared by the method described in JP H2-233626 A. Compound (3-1)is prepared by the method described in JP S59-176221 A. Compound (4-1)and compound (4-7) are prepared by the method described in JP H2-503441A. The antioxidant is commercially available. The compound representedby formula (6) where t is 1 is available from Sigma-Aldrich Corporation.Compound (6) where t is 7 and so forth are prepared according to themethod described in U.S. Pat. No. 3,660,505 B.

Any compounds whose synthetic methods are not described above can beprepared by the methods described in books such as Organic Syntheses(John Wiley & Sons, Inc.), Organic Reactions (John Wiley & Sons,Inc-Comprehensive Organic Synthesis (Pergamon Press), New ExperimentalChemistry Course (Shin Jikken Kagaku Koza in Japanese) (Maruzen Co.,Ltd.) and so forth. The composition is prepared according to a publiclyknown method using the thus obtained compounds. For example, thecomponent compounds are mixed and dissolved in each other by heating.

Last, the application of the composition will be described. Thecomposition of the invention mainly has a minimum temperature ofapproximately −10° C. or lower, a maximum temperature of approximately70° C. or higher and an optical anisotropy in the range of approximately0.07 to approximately 0.20. The composition having an optical anisotropyin the range of approximately 0.08 to approximately 0.25, and also thecomposition having an optical anisotropy in the range of approximately0.10 to approximately 0.30 may be prepared by controlling the ratio ofthe component compound or by mixing with any other liquid crystalcompound. A device including the composition has a large voltage holdingratio. The composition is suitable for use in the AM device. Thecomposition is particularly suitable for use in a transmissive AMdevice. The composition can be used as the composition having thenematic phase and as the optically active composition by adding theoptically active compound.

The composition can be used for the AM device. The composition can alsobe used for a PM device. The composition can be used for an AM deviceand a PM device having a mode such as PC, TN, STN, ECB, OCB, IPS, FFS,VA or FPA mode. Use for the AM device having TN, OCB, IPS mode or FFSmode is particularly preferred. In the AM device having the IPS mode orFFS mode, alignment of liquid crystal molecules in a state in which novoltage is applied may be parallel or perpendicular relative to a glasssubstrate. The devices may be of a reflective type, a transmissive typeor a transreflective type. Use for the transmissive device is preferred.The composition can also be used for an amorphous silicon-TFT device ora polycrystal silicon-TFT device. The composition can also be used for anematic curvilinear aligned phase (NCAP) mode device prepared bymicroencapsulating the composition and for a polymer dispersed (PD) modedevice in which a three-dimensional network polymer is formed in thecomposition.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the invention and specificexamples provided herein without departing from the spirit or scope ofthe invention. Thus, it is intended that the invention covers themodifications and variations of this invention that come within thescope of any claims and their equivalents.

The following examples are for illustrative purposes only and are notintended, nor should they be interpreted to, limit the scope of theinvention.

EXAMPLES

The invention will be described in greater details by way of Examples.The invention is not restricted by the Examples. The invention includesa mixture of a composition in Example 1 and a composition in Example 2.The invention also includes a mixture prepared by mixing at least twocompositions in Examples. A compound synthesized was identified by amethod such as NMR analysis. Characteristics of the compound and thecomposition were measured according to the methods described below.

NMR analysis: DRX-500 made by Bruker BioSpin Corporation was used formeasurement. In measurement of ¹H-NMR, a sample was dissolved in adeuterated solvent such as CDCl₃, and measurement was carried out underconditions of room temperature, 500 MHz and 16 times of accumulation.Tetramethylsilane was used as an internal standard. In measurement of¹⁹F-NMR, measurement was carried out using CFCl₃ as an internal standardand under 24 times of accumulation. In explanation of a nuclear magneticresonance spectrum, s, d, t, q, quin, sex and m stands for a singlet, adoublet, a triplet, a quartet, a quintet, a sextet and a multiplet andbr being broad, respectively.

Gas chromatographic analysis: GC-14B Gas Chromatograph made by ShimadzuCorporation was used for measurement. A carrier gas was helium (2milliliters per minute). A sample injector and a detector (FID) were setto 280° C. and 300° C., respectively. Capillary column DB-1 (length 30m, bore 0.32 mm, film thickness 0.25 μm, dimethylpolysiloxane as astationary phase, non-polar) made by Agilent Technologies, Inc. was usedfor separation of component compounds. After the column was kept at 200°C. for 2 minutes, the column was heated to 280° C. at a rate of 5° C.per minute. A sample was prepared in an acetone solution (0.1% byweight), and then 1 microliter of solution was injected into the sampleinjector. A recorder was Chromatopac Model C-R5A made by ShimadzuCorporation or the equivalent thereof. The resulting gas chromatogramshowed a retention time of a peak and each peak area corresponding tothe component compounds.

As a solvent for diluting the sample, chloroform, hexane and so forthmay also be used. The following capillary columns may also be used forseparating the component compounds: HP-1 (length 30 m, bore 0.32 mm,film thickness 0.25 μm) made by Agilent Technologies, Inc., Rtx-1(length 30 m, bore 0.32 mm, film thickness 0.25 μm) made by RestekCorporation and BP-1 (length 30 m, bore 0.32 mm, film thickness 0.25 μm)made by SGE International Pty. Ltd. A capillary column CBP1-M50-025(length 50 m, bore 0.25 mm, film thickness 0.25 μm) made by ShimadzuCorporation may also be used for the purpose of avoiding an overlap ofpeaks of the compounds.

A ratio of the liquid crystal compounds contained in the composition maybe calculated by the method described below. A mixture of liquid crystalcompounds is detected by gas chromatograph (FID). A ratio of the peakareas in the gas chromatogram corresponds to a ratio (weight ratio) ofthe liquid crystal compounds. When the capillary column described abovewas used, a correction coefficient of each liquid crystal compound maybe regarded as 1. Accordingly, the ratio (% by weight) of the liquidcrystal compounds can be calculated from the ratio of the peak areas.

Sample for measurement: When characteristics of a composition or adevice were measured, the composition was used as a sample as was. Whencharacteristics of a compound were measured, a sample for measurementwas prepared by mixing the compound (15% by weight) with a base liquidcrystal (85% by weight). Values of characteristics of the compound werecalculated using values obtained by measurement, according to anextrapolation method: (Extrapolated value)={(measured value of asample)−0.85×(measured value of base liquid crystal)}/0.15. When asmectic phase (or crystals) precipitated at 25° C., a ratio of thecompound to the base liquid crystal was changed step by step in theorder of (10% by weight:90% by weight), (5% by weight:95% by weight) and(1% by weight:99% by weight). Values of maximum temperature, opticalanisotropy, viscosity, and dielectric anisotropy with regard to thecompound were determined according to the extrapolation method.

The base liquid crystal as described below was used. A ratio of acomponent compound was expressed in terms of weight percent.

Measuring method: Characteristics were measured according to a methoddescribed below. Most of the measuring methods were applied as describedin the Standard of the Japan Electronics and Information TechnologyIndustries Association (hereinafter, abbreviated as JEITA) (JEITA EIAJED-2521B) discussed and established by JEITA, or modified thereon. Nothin film transistor (TFT) was attached to a TN device used formeasurement.

(1) Maximum temperature of a nematic phase (NI; ° C.): A sample was puton a hot plate in a melting point apparatus equipped with a polarizingmicroscope and was heated at a rate of 1° C. per minute. Temperaturewhen part of the sample began to change from a nematic phase to anisotropic liquid was measured.

(2) Minimum temperature of a nematic phase (T_(c); ° C.): samples eachhaving a nematic phase were put in glass vials and kept in freezers attemperatures of 0° C., −10° C., −20° C., −30° C. and −40° C. for 10days, and then liquid crystal phases were observed. For example, when asample maintained the nematic phase at −20° C. and changed to crystalsor a smectic phase at −30° C., T_(c) was expressed as T_(c)<−20° C.

(3) Viscosity (bulk viscosity; q; measured at 20° C.; mPa·s): Acone-plate type (E-type) rotational viscometer made by Tokyo Keiki Inc.was used for measurement.

(4) Viscosity (rotational viscosity; γ1; measured at 25° C.; mPa·s):Measurement was carried out according to the method described in M. Imaiet al., Molecular Crystals and Liquid Crystals, Vol. 259, p. 37 (1995).A sample was put in a TN device in which a twist angle was 0 degrees anda gap (cell gap) between two glass substrates was 5 micrometers. Voltagewas applied stepwise to the device in the range of 16 V to 19.5 V at anincrement of 0.5 V. After a period of 0.2 second with no voltage,voltage was applied repeatedly under the conditions of only onerectangular wave (rectangular pulse; 0.2 second) and no voltageapplication (2 seconds). A peak current and a peak time of a transientcurrent generated by the applied voltage were measured. A value ofrotational viscosity was obtained from the measured values and acalculation equation (8) described on page 40 of the paper presented byM. Imai et al. A value of dielectric anisotropy necessary for thecalculation was obtained by the method indicated below using the devicethat was used for measuring the rotational viscosity.

(5) Optical anisotropy (refractive index anisotropy; Δn; measured at 25°C.): Measurement was carried out by an Abbe refractometer with apolarizing plate on an ocular, using light at a wavelength of 589nanometers. A surface of a main prism was rubbed in one direction, andthen a sample was added dropwise on the main prism. A refractive index(n∥) was measured when the direction of polarized light was parallel tothe direction of rubbing. A refractive index (n⊥) was measured when thedirection of polarized light was perpendicular to the direction ofrubbing. A value of optical anisotropy was calculated from an equation:Δn=n∥−n⊥.

(6) Dielectric anisotropy (ΔE; measured at 25° C.): A sample was putinto a TN device in which a distance (cell gap) between two glasssubstrates was 9 micrometers and a twist angle was 80 degrees. Sinewaves (10 V, 1 kHz) were applied to the device, and after 2 seconds, adielectric constant (∈∥) in the major axis direction of the liquidcrystal molecules was measured. Sine waves (0.5 V, 1 kHz) were appliedto the device, and after 2 seconds, a dielectric constant (∈⊥) in theminor axis direction of the liquid crystal molecules was measured. Avalue of dielectric anisotropy was calculated from an equation:Δ∈=∈∥−∈⊥.

(7) Threshold voltage (Vth; measured at 25° C.; V): An LCD 5100luminance meter made by Otsuka Electronics Co., Ltd. was used formeasurement. A light source was a halogen lamp. A sample was put in anormally white mode TN device in which a distance (cell gap) between twoglass substrates was 0.45/Δn (μm) and a twist angle was 80 degrees. Avoltage (32 Hz, rectangular wave) to be applied to the device wasincreased stepwise from 0 V to 10 V at an increment of 0.02 V. In theabove case, the device was irradiated with light from a directionperpendicular to the device, and an amount of light transmitted throughthe device was measured. A voltage-transmittance curve was prepared, inwhich the maximum amount of light corresponds to 100% transmittance andthe minimum amount of light corresponds to 0% transmittance. A thresholdvoltage is a voltage at 90% transmittance.

(8) Voltage holding ratio (VHR-1; measured at 25° C.; %): A TN deviceused for measurement had a polyimide alignment film, and a distance(cell gap) between two glass substrates was 5 micrometers. A sample wasput in the device, and then the device was sealed with anultraviolet-curable adhesive. A pulse voltage (60 microseconds at 5 V)was applied to the TN device and the device was charged. A decayingvoltage was measured for 16.7 milliseconds with a high-speed voltmeter,and area A between a voltage curve and a horizontal axis in a unit cyclewas determined. Area B was an area without decay. A voltage holdingratio was expressed as a percentage of area A to area B.

(9) Voltage holding ratio (VHR-2; measured at 80° C.; %): A voltageholding ratio was measured in a manner identical with the procedures asdescribed above except that measurement was carried out at 80° C. inplace of 25° C. The value obtained was described in terms of VHR-2.

(10) Voltage holding ratio (VHR-3; measured at 25° C.; %): Stability toultraviolet light was evaluated by measuring a voltage holding ratioafter a device was irradiated with ultraviolet light. A TN device usedfor measurement had a polyimide alignment film, and a cell gap was 5micrometers. A sample was injected into the device, and then the devicewas irradiated with light for 20 minutes. A light source was ultra-highpressure mercury lamp USH-500D (made by Ushio, Inc.), and a distancebetween the device and the light source was 20 centimeters. In measuringVHR-3, a decaying voltage was measured for 16.7 milliseconds. Acomposition having a large VHR-3 has a large stability to ultravioletlight. A value of VHR-3 is preferably 90% or more, further preferably,95% or more.

(11) Voltage holding ratio (VHR-4; measured at 25° C.; %): A TN deviceinto which a sample was injected was heated in a constant temperaturebath at 80° C. for 500 hours, and then stability to heat was evaluatedby measuring a voltage holding ratio. In measuring VHR-4, a decayingvoltage was measured for 16.7 milliseconds. A composition having a largeVHR-4 has a large stability to heat.

(12) Response time (τ; measured at 25° C.; ms): An LCD5100 luminancemeter made by Otsuka Electronics Co., Ltd. was used for measurement. Alight source was a halogen lamp. A low-pass filter was set at 5 kHz. Asample was put into a normally white mode TN device in which a distance(cell gap) between two glass substrates was 5.0 micrometers and a twistangle was 80 degrees. Rectangular waves (60 Hz, 5 V, 0.5 seconds) wereapplied to the device. On the occasion, the device was irradiated withlight from a direction perpendicular to the device, and an amount oflight transmitted through the device was measured. The maximum amount oflight corresponds to 100% transmittance, and the minimum amount of lightcorresponds to 0% transmittance. A rise time (τr: ms) is a period oftime needed for a change from 90% transmittance to 10% transmittance. Afall time (τf: fall time; ms) is a period of time needed for a changefrom transmittance 10% to 90% transmittance. A response time is a sum ofthe rise time and the fall time thus obtained.

(13) Elastic constant (K; measured at 25° C.; pN): HP4284A LCR Meter byYokogawa-Hewlett-Packard Co. was used for measurement. A sample was putinto a horizontal alignment device in which a distance (cell gap)between two glass substrates was 20 micrometers. Voltage from 0 V to 20V was applied to the device, and electrostatic capacity and the appliedvoltage were measured. Measured values of the capacitance (C) and theapplied voltage (V) were fitted to equation (2.98) and equation (2.101)on page 75 of “Liquid Crystal Device Handbook (Ekisho Debaisu Handobukkuin Japanese)” (Nikkan Kogyo Shimbun, Ltd.), and values of K11 and K33were obtained from equation (2.99). Next, K22 was calculated using thevalue of K11 and K33 in equation (3.18) on page 171 of the samehandbook. An elastic constant is a mean value of the thus determinedK11, K22 and K33.

(14) Specific resistance (ρ; measured at 25° C.; Ωcm): Into a vesselequipped with electrodes, 1.0 milliliter of a sample was injected. A DCvoltage (10 V) was applied to the vessel, and a DC current after 10seconds was measured. A specific resistance was calculated from thefollowing equation: (specific resistance)={(voltage)×(electric capacityof a vessel)}/{(direct current)×(dielectric constant of vacuum)}.

(15) Helical pitch (P; measured at room temperature; μm): A helicalpitch was measured according to a wedge method. Refer to “Handbook ofLiquid Crystals (Ekisho Binran in Japanese),” page 196, (issued in 2000,Maruzen Co., Ltd.). A sample was injected into a wedge cell and left tostand at room temperature for 2 hours, and then a gap (d2−d1) betweendisclination lines was observed by a polarizing microscope (trade name:MM40/60 series, Nikon Corporation). A helical pitch (P) was calculatedaccording to the following equation in which an angle of the wedge cellwas expressed as θ: P=2×(d2−d1)×tan θ.

(16) Dielectric constant in a minor axis direction (∈⊥; measured at 25°C.): A sample was put into a TN device in which a distance (cell gap)between two glass substrates is 9 micrometers and a twist angle is 80degrees. Sine waves (0.5 V, 1 kHz) were applied to the device, and adielectric constant (∈⊥) in a minor axis direction of the liquid crystalmolecules was measured after 2 seconds.

(17) DC brightness relaxation time constant (τ_(DC); measured at 50° C.;%/s): Although a method of measuring the time constant is described inPatent literature No. 1, a simplified method was applied here.Multimedia Display Tester 3298F by Yokogawa Electric Corporation wasused for measurement. A light source was a halogen lamp. First, a samplewas put into an FFS device in which a distance (cell gap) between twoglass substrates was 3.2 micrometers. A DC voltage from 0 V to 10 V wasapplied to the device, and a voltage (V_(21.1)) at which an amount oflight transmitted through the device became 21.1% being the maximum (127gradations) was measured. Next, a voltage obtained by adding an offsetvoltage (DC1V) to the voltage above was applied to the device, and anamount of light transmitted through the device was measured for 300seconds until the amount of light became constant. The results wereplotted and a DC brightness relaxation time constant was determined froman inclination of a straight line from 0 seconds to 60 seconds. As thevalue is negatively larger, discharge of electric charge accumulated ina picture element is faster, and therefore image persistence reduces.

Compounds in Examples and Comparative Examples were described usingsymbols according to definitions in Table 3 below. In Table 3, aconfiguration of 1,4-cyclohexylene is trans. Parenthesized number nextto a symbolized compound corresponds to the number of the compound. Asymbol (-) means any other liquid crystal compound. A ratio (percentage)of the liquid crystal compound is expressed in terms of weight percent(% by weight) based on the weight of the liquid crystal composition.Values of characteristics of the composition were summarized in the lastpart.

TABLE 3 Method for Description of Compounds using SymbolsR—(A₁)—Z₁ - - - Z_(n)—(A_(n))—R′ 1) Left-terminal Group R— SymbolC_(n)H_(2n+1)— n— C_(n)H_(2n+1)O— nO— C_(m)H_(2m+1)OC_(n)H_(2n)— mOn—CH₂═CH— V— C_(n)H_(2n+1)—CH═CH— nV— CH₂═CH—C_(n)H_(2n)— Vn—C_(m)H_(2m+1)—CH═CH—C_(n)H_(2n)— mVn— CF₂═CH— VFF— CF₂═CH—C_(n)H_(2n)—VFFn— F—C_(n)H_(2n)— Fn— 2) Right-terminal Group —R′ Symbol—C_(n)H_(2n+1) —n —OC_(n)H_(2n+1) —On —CH═CH₂ —V —CH═CH—C_(n)H_(2n+1)—Vn —C_(n)H_(2n)—CH═CH₂ —nV —C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) —nVm—CH═CF₂ —VFF —COOCH₃ —EMe —F —F —Cl —CL —OCF₃ —OCF3 —CF₃ —CF3 —CN —C 3)Bonding Group —Zn— Symbol —C₂H₄— 2 —COO— E —CH═CH— V —C≡O— T —CF₂O— X—CH₂O— 1O 4) Ring Structure —A_(n)— Symbol

H

Dh

dh

B

B(F)

B(2F)

B(F,F)

B(2F,5F)

G

Py

B(2F,3F) 5) Examples of Description Example 1 V-HHB-1

Example 2 3-BB(F)B(F,F)—F

Example 3 4-BB(F)B(F,F)XB(F,F)—F

Example 4 5-GB(F,F)XB(F,F)—F

Example 1

3-HHXB(F,F)-F (2-4) 10% 3-HHXB(F,F)-CF3 (2-5) 3% 2-HHBB(F,F)-F (2-19) 4%3-HHBB(F,F)-F (2-19) 5% 4-HHBB(F,F)-F (2-19) 4% 5-HHBB(F,F)-F (2-19) 4%4-GB(F)B(F,F)XB(F,F)-F (2-27) 7% 3-BB(F)B(F,F)XB(F)-F (2-28) 4%3-BB(F)B(F,F)XB(F,F)-F (2-29) 3% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 8%5-BB(F)B(F,F)XB(F,F)-F (2-29) 6% 3-HH-V (3-1) 30% 4-HH-V1 (3-1) 5%7-HB-1 (3-2) 3% 3-HHB-O1 (3-5) 4%

NI=107.1° C.; Tc<−20° C.; Δn=0.113; Δ∈=11.2; Vth=1.45 V; η=16.8 mPa·s;γ1=102.9 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.051%/s.

Comparative Example 1

A DC brightness relaxation time constant was measured on a compositionbefore compound (1-1) in Example 1 was added. τ_(DC)=−0.024%/s.

Example 2

4-GHB(F,F)-F (2-7) 5% 3-GB(F)B(F)-F (2-11) 5% 3-GB(F,F)XB(F)-F (2-13) 4%2-HHBB(F,F)-F (2-19) 4% 3-HHBB(F,F)-F (2-19) 6% 4-HHBB(F,F)-F (2-19) 5%4-GB(F)B(F,F)XB(F,F)-F (2-27) 7% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 9%5-BB(F)B(F,F)XB(F,F)-F (2-29) 7% 3-HHB-CL (2) 3% 3-HH-V (3-1) 29%3-HH-VFF (3-1) 4% 3-HB-O2 (3-2) 3% 3-HHB-3 (3-5) 3% 5-HBB-2 (3-6) 3%3-HBBH-1O1 (—) 3%

NI=104.1° C.; Tc<−20° C.; Δn=0.114; Δ∈=10.9; Vth=1.55 V; η=16.9 mPa·s;γ1=112.1 mPa·s; VHR-1=99.2%; VHR-2=98.2%; VHR-3=98.1%. To thecomposition, compound (1-1) was added in a ratio of 0.1% by weight, anda DC brightness relaxation time constant was measured. τ_(DC)=−0.061%/s.

Example 3

3-HHXB(F,F)-F (2-4) 11% 3-HGB(F,F)-F (2-6) 3% 4-GHB(F,F)-F (2-7) 10%3-BB(F,F)XB(F,F)-F (2-18) 9% 2-HHEB(F,F)-F (2-19) 4% 3-HHBB(F,F)-F(2-19) 5% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 9% 5-BB(F)B(F,F)XB(F,F)-F (2-29)3% 3-HB(2F,3F)BXB(F,F)-F (2-34) 10% 3-HH-V (3-1) 20% 1-BB-5 (3-3) 5%3-HHB-1 (3-5) 8% 3-HBB-2 (3-6) 3%

NI=94.9° C.; Tc<−20° C.; Δn=0.113; Δ∈=12.1; Vth=1.44 V; η=18.1 mPa·s;γ1=113.4 mPa·s. To the composition, compound (1-2) was added in a ratioof 0.08% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.053%/s.

Example 4

3-HHB(F,F)-F (2-2) 3% 3-HHXB(F,F)-F (2-4) 13% 3-HB(F)B(F,F)-F (2-9) 5%3-BB(F)B(F,F)-F (2-15) 13% 3-HHBB(F,F)-F (2-19) 3% 4-GBB(F)B(F,F)-F(2-22) 3% 3-HBBXB(F,F)-F (2-23) 8% 3-HBB(F,F)XB(F,F)-F (2-24) 6%3-BB(2F,3F)BXB(F,F)-F (2-35) 3% 3-HH-V (3-1) 24% 3-HH-V1 (3-1) 7%V2-BB-1 (3-3) 3% 3-HHEH-3 (3-4) 3% 1-BB(F)B-2V (3-7) 3% 5-HBB(F)B-2(3-13) 3%

NI=93.7° C.; Tc<−20° C.; Δn=0.121; Δ∈=7.5; Vth=1.59 V; η=18.5 mPa·s;γ1=97.6 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.07% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.052%/s.

Example 5

5-HXB(F,F)-F (2-1) 5% 3-HHB(F,F)-F (2-2) 10% 3-HHEB(F,F)-F (2-3) 9%3-HHXB(F,F)-F (2-4) 13% 2-HBEB(F,F)-F (2-10) 3% 3-HBEB(F,F)-F (2-10) 3%3-BBXB(F,F)-F (2-17) 3% 3-BB(F,F)XB(F,F)-F (2-18) 7%3-dhBB(F,F)XB(F,F)-F (2-25) 4% 3-BB(F)B(F,F)XB(F)B(F,F)-F (2-31) 3%3-HB-CL (2) 6% 3-HH-V (3-1) 7% 3-HH-V1 (3-1) 10% 5-HH-V (3-1) 7%3-HHEBH-3 (3-10) 4% 3-BB(2F,3F)-O2 (4-5) 3% 3-dhBB(2F,3F)-O2 (4-16) 3%

NI=77.8° C.; Tc<−20° C.; Δn=0.090; Δ∈=9.1; Vth=1.19 V; η=17.8 mPa·s;γ1=86.2 mPa·s. To the composition, compound (1-2) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.053%/s.

Example 6

3-GB(F,F)XB(F,F)-F (2-14) 4% 3-BB(F)B(F,F)-CF3 (2-16) 3%3-BB(F,F)XB(F,F)-F (2-18) 16% 3-HHB(F)B(F,F)-F (2-20) 4% 3-HBBXB(F,F)-F(2-23) 10% 4-GB(F)B(F,F)XB(F,F)-F (2-27) 4% 5-GB(F)B(F,F)XB(F,F)-F(2-27) 4% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 4% 3-B(2F,3F)BXB(F,F)-F (2-33)3% 3-HH-V (3-1) 25% 3-HH-O1 (3-1) 3% 1-BB-3 (3-3) 3% V-HHB-1 (3-5) 5%2-BB(F)B-3 (3-7) 3% 5-B(F)BB-2 (3-8) 3% V-HHB(2F,3F)-O2 (4-7) 3%3-HBB(2F,3F)-O2 (4-15) 3%

NI=71.2° C.; Tc<−20° C.; Δn=0.120; Δ∈=11.9; Vth=1.24 V; η=18.2 mPa·s;γ1=89.8 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.12% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.070%/s.

Example 7

3-HBB(F,F)-F (2-8) 4% 3-GB(F)B(F,F)-F (2-12) 3% 3-BB(F)B(F,F)-F (2-15)6% 3-BB(F,F)XB(F,F)-F (2-18) 18% 3-HBBXB(F,F)-F (2-23) 3%3-BB(F)B(F,F)XB(F,F)-F (2-29) 3% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 7%4-BB(F,F)XB(F)B(F,F)-F (2-30) 3% 3-HH-V (3-1) 29% V-HHB-1 (3-5) 11%2-BB(F)B-2V (3-7) 4% 3-HB(F)HH-5 (3-9) 3% 5-HBBH-3 (3-11) 3% 3-HB(F)BH-3(3-12) 3%

NI=80.6° C.; Tc<−30° C.; Δn=0.124; Δ∈=9.9; Vth=1.54 V; η=20.6 mPa·s;γ1=81.1 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.060%/s.

Example 8

3-HHXB(F,F)-F (2-4) 10% 4-GHB(F,F)-F (2-7) 10% 3-BB(F,F)XB(F,F)-F (2-18)6% 2-HHBB(F,F)-F (2-19) 4% 3-HHBB(F,F)-F (2-19) 6% 4-HHBB(F,F)-F (2-19)5% 5-HHBB(F,F)-F (2-19) 5% 3-GBB(F)B(F,F)-F (2-22) 3%4-GB(F)B(F,F)XB(F)-F (2-26) 8% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 3% 3-HH-V(3-1) 19% 2-HH-3 (3-1) 4% 3-HH-4 (3-1) 3% V2-BB-1 (3-3) 6% 3-HHB-1 (3-5)5% 5-HBB(F)B-3 (3-13) 3%

NI=107.6° C.; Tc<−20° C.; Δn=0.111; Δ∈=10.6; Vth=1.55 V; η=19.4 mPa·s;γ1=121.9 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.064%/s.

Example 9

3-HHXB(F,F)-CF3 (2-5) 12% 3-GB(F,F)XB(F,F)-F (2-14) 8% 3-GBB(F)B(F,F)-F(2-22) 3% 4-GBB(F)B(F,F)-F (2-22) 3% 3-HBBXB(F,F)-F (2-23) 3%4-GB(F)B(F,F)XB(F,F)-F (2-27) 5% 5-GB(F)B(F,F)XB(F,F)-F (2-27) 5%4-BB(F)B(F,F)XB(F,F)-F (2-29) 7% 5-BB(F)B(F,F)XB(F,F)-F (2-29) 5% 3-HH-V(3-1) 22% 3-HH-V1 (3-1) 10% 3-HH-2V1 (3-1) 9% V2-HHB-1 (3-5) 8%

NI=89.7° C.; Tc<−20° C.; Δn=0.102; Δ∈=13.7; Vth=1.35 V; η=20.6 mPa·s;γ1=126.5 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.067%/s.

Example 10

3-HHB(F,F)-F (2-2) 10% 3-HHXB(F,F)-F (2-4) 3% 3-GHB(F,F)-F (2-7) 4%3-BB(F)B(F,F)-F (2-15) 7% 3-BB(F,F)XB(F,F)-F (2-18) 13%3-GB(F)B(F)B(F)-F (2-21) 6% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 10% 3-HH-V(3-1) 17% 3-HH-4 (3-1) 11% 5-HB-O2 (3-2) 3% 3-HHB-1 (3-5) 5% 3-HHB-O1(3-5) 6% 3-HHB-3 (3-5) 5%

NI=83.1° C.; Tc<−20° C.; Δn=0.109; Δ∈=9.9; Vth=1.42 V; η=19.6 mPa·s;γ1=114.3 mPa·s. To the composition, compound (1-2) was added in a ratioof 0.08% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.052%/s.

Example 11

3-BB(F,F)XB(F,F)-F (2-18) 5% 2-HHBB(F,F)-F (2-19) 2% 3-HHBB(F,F)-F(2-19) 3% 4-HHBB(F,F)-F (2-19) 4% 4-BB(F)B(F,F)XB(F,F)-F (2-29) 4%5-BB(F)B(F,F)XB(F,F)-F (2-29) 2% 3-BB(2F,3F)XB(F,F)-F (2-32) 5% 3-HB-CL(2) 6% 3-HHB-CL (2) 6% 5-HHB-CL (2) 5% 3-HH-V1 (3-1) 10% 4-HH-V (3-1)13% 5-HH-V (3-1) 10% V-HHB-1 (3-5) 13% 2-BB(F)B-3 (3-7) 5% 2-BB(F)B-5(3-7) 4% 5-HBB(F)B-2 (3-13) 3%

NI=102.2° C.; Tc<−20° C.; Δn=0.117; Δ∈=4.5; Vth=2.19 V; η=17.8 mPa·s;γ1=85.4 mPa·s. To the composition, compound (1-1) was added in a ratioof 0.1% by weight, and a DC brightness relaxation time constant wasmeasured. τ_(DC)=−0.056%/s.

The DC brightness relaxation time constant in Comparative Example 1 was−0.024%/s. On the other hand, the DC brightness relaxation timeconstants in Example 1 to Example 11 each were in the range from−0.051%/s to −0.070%/s. Thus, the compositions in Examples each have anegatively larger DC brightness relaxation time constant in comparisonwith the composition in Comparative Example. Accordingly, the liquidcrystal composition according to the invention is concluded to havefurther excellent characteristics.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the disclosure has beenmade only by way of example, and that numerous changes in the conditionsand order of steps can be resorted to by those skilled in the artwithout departing from the spirit and scope of the invention.

INDUSTRIAL APPLICABILITY

A liquid crystal composition of the invention satisfies at least one ofcharacteristics such as a high maximum temperature, a low minimumtemperature, a small viscosity, a suitable optical anisotropy, a largedielectric anisotropy, a large specific resistance, a large elasticconstant, a high stability to ultraviolet light and a high stability toheat, or has a suitable balance regarding at least two of thecharacteristics. A liquid crystal display device including thecomposition has a short response time, a large voltage holding ratio, alarge contrast ratio, a large DC brightness relaxation time constant, along service life and so forth, and thus can be used for a liquidcrystal projector, a liquid crystal television and so forth.

What is claimed is:
 1. A liquid crystal composition that has a positivedielectric anisotropy and a nematic phase, and contains at least onecompound selected from the group of compounds represented by formula (1)as an additive component and at least one compound from the group ofcompounds represented by formula (2) as a first component:

wherein, in formula (1), R¹ is hydrogen or alkyl having 1 to 15 carbons;R², R³, R⁴ and R⁵ are independently hydrogen or alkyl having 1 to 4carbons; ring A is a polyvalent group derived from benzene orcyclohexane by eliminating hydrogen; a is 3 or 4; and in formula (2), R⁶is alkyl having 1 to 12 carbons, alkoxy having to 12 carbons or alkenylhaving 2 to 12 carbons; ring B is 1,4-cyclohexylene, 1,4-phenylene,2-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene,2,6-difluoro-1,4-phenylene, pyrimidine-2,5-diyl, 1,3-dioxane-2,5-diyl ortetrahydropyran-2,5-diyl; Z¹ is a single bond, ethylene, carbonyloxy ordifluoromethyleneoxy; X¹ and X² are independently hydrogen or fluorine;Y¹ is fluorine, chlorine, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, alkoxy having 1 to12 carbons in which at least one of hydrogen is replaced by fluorine orchlorine, or alkenyloxy having 2 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; and b is 1, 2, 3 or
 4. 2.The liquid crystal composition according to claim 1, containing acompound represented by formula (1-1) or formula (1-2) as the additivecomponent:


3. The liquid crystal composition according to claim 1, wherein a ratioof the additive component is in the range of 0.005% by weight to 1% byweight based on the weight of the liquid crystal composition.
 4. Theliquid crystal composition according to claim 1, containing at least onecompound selected from the group of compounds represented by formula(2-1) to (2-35) as the first component:

wherein, in formula (2-1) to (2-35), R⁶ is alkyl having 1 to 12 carbons,alkoxy having 1 to 12 carbons or alkenyl having 2 to 12 carbons.
 5. Theliquid crystal composition according to claim 1, wherein a ratio of thefirst component is in the range of 10% by weight to 90% by weight basedon the weight of the liquid crystal composition.
 6. The liquid crystalcomposition according to claim 1, containing at least one compoundselected from the group of compounds represented by formula (3) as asecond component:

wherein, in formula (3), R⁷ and R⁸ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, alkyl having 1 to 12 carbons in which at least one of hydrogenis replaced by fluorine or chlorine, or alkenyl having 2 to 12 carbonsin which at least one of hydrogen is the replaced by fluorine orchlorine; ring C and ring D are independently 1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene or 2,5-difluoro-1,4-phenylene; Z²is a single bond, ethylene or carbonyloxy; and c is 1, 2 or
 3. 7. Theliquid crystal composition according to claim 6, containing at least onecompound selected from the group of compounds represented by formula(3-1) to (3-13) as the second component:

wherein, in formula (3-1) to formula (3-13), R⁷ and R⁸ are independentlyalkyl having 1 to 12 carbons, alkoxy having 1 to 12 carbons, alkenylhaving 2 to 12 carbons, alkyl having 1 to 12 carbons in which at leastone of hydrogen is replaced by fluorine or chlorine, or alkenyl having 2to 12 carbons in which at least one of hydrogen is replaced by fluorineor chlorine.
 8. The liquid crystal composition according to claim 6,wherein a ratio of the second component is in the range of 10% by weightto 90% by weight based on the weight of the liquid crystal composition.9. The liquid crystal composition according to claim 1, containing atleast one compound selected from the group of compounds represented byformula (4) as a third component:

wherein, in formula (4), R⁹ and R¹⁰ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; ring E and ring G areindependently 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene,1,4-phenylene in which at least one of hydrogen is replaced by fluorineor chlorine, or tetrahydropyran-2,5-diyl; ring F is2,3-difluoro-1,4-phenylene, 2-chloro-3-fluoro-1,4-phenylene,2,3-difluoro-5-methyl-1,4-phenylene, 3,4,5-trifluoronaphthalene-2,6-diylor 7,8-difluorochroman-2,6-diyl; Z³ and Z⁴ are independently a singlebond, ethylene, carbonyloxy or methyleneoxy; d is 1, 2 or 3, and e is 0or 1; and a sum of d and e is 3 or less.
 10. The liquid crystalcomposition according to claim 9, containing at least one compoundselected from the group of compounds represented by a formula (4-1) toformula (4-21) as the third component:

wherein, in formula (4-1) to formula (4-21), R⁹ and R¹⁰ areindependently alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, alkenyloxy having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine.
 11. The liquid crystalcomposition according to claim 9, wherein a ratio of the third componentis in the range of 3% by weight to 25% by weight based on the weight ofthe liquid crystal composition.
 12. The liquid crystal compositionaccording to claim 6, containing at least one compound selected from thegroup of compounds represented by formula (4) as a third component:

wherein, in formula (4), R⁹ and R¹⁰ are independently alkyl having 1 to12 carbons, alkoxy having 1 to 12 carbons, alkenyl having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine; ring E and ring G areindependently 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene,1,4-phenylene in which at least one of hydrogen is replaced by fluorineor chlorine, or tetrahydropyran-2,5-diyl; ring F is2,3-difluoro-1,4-phenylene, 2-chloro-3-fluoro-1,4-phenylene,2,3-difluoro-5-methyl-1,4-phenylene, 3,4,5-trifluoronaphthalene-2,6-diylor 7,8-difluorochroman-2,6-diyl; Z³ and Z⁴ are independently a singlebond, ethylene, carbonyloxy or methyleneoxy; d is 1, 2 or 3, and e is 0or 1; and a sum of d and e is 3 or less.
 13. The liquid crystalcomposition according to claim 12, containing at least one compoundselected from the group of compounds represented by a formula (4-1) toformula (4-21) as the third component:

wherein, in formula (4-1) to formula (4-21), R⁹ and R¹⁰ areindependently alkyl having 1 to 12 carbons, alkoxy having 1 to 12carbons, alkenyl having 2 to 12 carbons, alkenyloxy having 2 to 12carbons, or alkyl having 1 to 12 carbons in which at least one ofhydrogen is replaced by fluorine or chlorine.
 14. The liquid crystalcomposition according to claim 12, wherein a ratio of the thirdcomponent is in the range of 3% by weight to 25% by weight based on theweight of the liquid crystal composition.
 15. The liquid crystalcomposition according to claim 1, wherein a maximum temperature of anematic phase is 70° C. or higher, optical anisotropy (measured at 25°C.) at a wavelength of 589 nanometers is 0.07 or more, and dielectricanisotropy (measured at 25° C.) at a frequency of 1 kHz is 2 or more.16. A liquid crystal display device, including the liquid crystalcomposition according to claim
 1. 17. The liquid crystal display deviceaccording to claim 16, wherein an operating mode of the liquid crystaldisplay includes a TN mode, an ECB mode, an OCB mode, an IPS mode, anFFS mode or an FPA mode, and a driving mode of the liquid crystaldisplay device includes an active matrix mode.